1. Field of the Invention
The present invention relates to an edge generation method, an edge generation device, a medium recording edge generation program, and an image processing method.
2. Description of the Related Art
Heretofore, in generation of an enlarged image that results from increasing the number of structural pixels of an image that is not yet subjected to expansion in size (hereinafter referred to also as “unenlarged image”), a position of an edge is detected in a pixel of the unenlarged image. Then, the detected position of the edge is made to correspond to a pixel of the enlarged image to form an area of the edge of the enlarged image. Also, gradation data of each pixel of the enlarged image (hereinafter referred to also as “gradation data of enlarged image”) is generated through predetermined interpolation. In the interpolation using a bi-linear method, a bi-cubic method or the like, the gradation data of the enlarged image is generated by using image data of plural pixels within a predetermined area in the unenlarged image that is positioned in proximity to an intended pixel on the enlarged image. Then, the interpolation is conducted in blocks that sectionalize the pixels of the enlarged image in correspondence with the pixels of the unenlarged image to generate the gradation data of the enlarged image. Also, the edge is emphasized and sharpened on the basis of the image data of the unenlarged image so that the edge portion becomes sharpened.
Also, when it is judged that any one of an extent of variation of a gradation value of the intended pixel and an extent of variation of a gradation value of a pixel that is in proximity to the intended pixel meets a predetermined condition, the degree of variation is evaluated assuming that the intended pixel meets that condition, and one interpolation is selected from plural kinds of interpolations on the basis of the evaluation to execute pixel interpolation (for example, refer to Japanese Patent No. 3045134).
In the case where the position of the edge is detected in the pixel of the unenlarged image, a precision in the edge position of the enlarged image is not high, and a zigzag pattern that is so-called “jaggy” is highly visible on the edge of the enlarged image. Under the above circumstances, it is desired that the precision in the edge position is improved, and the edge of the enlarged image is formed with high precision and a thin line to facilitate sharpening or the like.
Also, it is desired that a characteristic portion such as a flesh color is excellently expressed while the image quality of other portions is maintained, and the edge portion is more excellently sharpened to make the processed image high in quality.
In addition, when interpolation is conducted by using the image data of plural pixels that straddle the area of the edge, the image data of a pixel that is at an opposite side of the area of the edge with respect to the intended pixel is reflected by the gradation data that has been subjected to interpolation. As a result, there arises such a problem that the edge portion is smoothed and blurred. In particular, in the case where interpolation is conducted in the block, when the blocks having the edge are sharpened, there arises such a problem that a color difference occurs between blocks where the area of the edge exists (hereinafter referred to also as “edge block” and blocks where no area of the edge exists (hereinafter referred to as “non-edge block”). In Japanese Patent No. 3045134, when cubic convolution interpolation is conducted by using the image data of plural pixels that straddle the area of the edge, the edge portion is smoothed. Under the above circumstances, it is desired that the sharpness of the edge portion is maintained to improve the image quality.